GTN-650 installation on Danish Cessna 172

We had been looking for a while to change the KX155 to another radio for 8.33 spacing. I have had advise from the forum and searched for a kx165 but had difficulties finding one.We then decided to install a GNC255.It was then clear that this could also be an opportunity to change the GPS for a GPS/Nav/com to get all in one package and to be able to operate the new GPS approaches. We looked deep in the pocket and decided to change the existing KX155, KLN94 and an annunciation unit for the GTN650 – hoping to be able to sell of the old equipment.We contacted a few local avionics shops but they didn’t seem interested to do the job. We then agreed with Jesse from this forum to fly down to Midden Zeeland, take some days off and let him do the job.The other group member flew the aircraft down to be ready for work on the Monday.This was at the same time of very nice summer weather so some days were spend at the local beaches. Midden Zeeland is a smaller airport with a grass runway, but with a manned tower, workshops and other activities. They were very accomodating in finding a rental car and Jesse had helped to find a local economic place to stay.The only problem during the install was a needed change of the altitude encoder. We had one with a resolution off 100 feet but need one that were more precise and approved together with the GTN650.Thursday I drove in car down from Denmark and switched – as we had agreed that one should fly down the other back. I arrived to meet Jesse for the first time and to see the avionics stack in a mess of wires.

Friday evening the aircraft was finished just short before the airfield closes at 20.00. Everything is now nicely stacked and Jesse found a good solution to cover the old place where the DME were. It was to late to fly it home that day, so had to wait till saturday morning.We had talked about a flight test, but the weather was getting worse on saturday morning and I could see that everything passed a comprehensive test in the work shop so I decided just to depart before the weather got to bad. I had used the evening in the hotel to read the manual to have a chance to find home.After startup it was first at the run-up point I discovered that the RPM was not showing. I taxied back and Jesse quickly pulled the cowling off. We then saw that the cable from the tachometer to the engine was not attached anymore on the engine side and it had been sligtly pulled out during the avionics work. Jesse recrimped the cable back on the nut and repair was done in a short time.Before takeof the aircraft had been on ground power and I have had time to put in the flight plan. The unit is much easier to operate than the old KLN94.The first part was a bit of scud-running but I knew the weather was set to improve along the route. I noticed some bird areas along the route and remembered the horror story about dutch airspace, being to low and bird areas.

Just when checking in with Dutch Mil I saw an opening and quickly arranged with them a climb to get on top of the muck.

I progressivly climbed and got a better share of the nice tail wind. As documented I’m now a member of the 150kt club!

After dodging a few Cumulus clouds in German airspace the sky got more or less clear and I had more time to play with the new GPS. I think most of it is quite straight forward but I still don’t understand that when it warns about airspace ahead there is no mentioning of any details about that airspace. I tried pressing the message but nothing happened. At the KLN94 it would mention the name of the airspace you are about to enter. The skydemon will even give frequencies etc.

We have for a long time had some issues with the KAP140 not arriving at the correct altitude using the ALTARM function. I think this changed quite a lot now since we now have amore precise (and reliable) altitude encoder. When flying home the altitude was spot on!This is a picture of the new stack taken on the trip home.